Employing pressure switches in sensing edges for doors is generally known. Such sensing edges generally include a sheath having several openings or chambers therein in fluid communication with each other, in order to transmit therebetween pressure changes in response to the application of external pressure to the sheath. The problem associated with such edges, is that in order to construct several openings or chambers in fluid communication with each other, a plurality of different types and structures of foam must be used within the sheath to provide the proper sensitivity and path to communicate the pressure changes therebetween. Therefore, constructing and assembling door edges of this type is costly.
Other types of more conventional door edges include a pair of upper or lower, flexible, electrically conductive sheets (e.g., aluminum foil) positioned on the upper and lower sides of a bridge. Upon application of pressure to the sheath, the conductive sheets are deflected into electrically conductive engagement with each other to thereby function as a switch to actuate suitable control circuitry for controlling the door. Sensing edges with this type of construction may not be as sensitive as that contemplated by the present invention. For instance, before the control circuitry is actuated, the conductive sheets must travel the full distance therebetween, in order to make an electrical connection. Moreover, forces which are applied to the sides of the sheath will not necessarily cause the electrically conductive sheets to deflect into engagement with each other to actuate the switch.
Generally, in switches of this type, there is required a highly localized deflection to operate the switch. Even a substantial force or weight may not be sufficient to actuate such a switch, if the force or weight is distributed over a substantial area. In an attempt to obviate this problem, such switches often include internal protrusions for locally enhancing internal forces reacting to an external weight. This structure adds to the cost of the materials, complexity of manufacture, and often inhibits or reduces flexibility and, therefore, requires additional space for shipping and storage.
Consequently, there exists a need for a high profile sensing edge to improve over travel compensation. There further exists a need for a sensing edge which will respond to forces applied anywhere along the surface of the sheath, including sideward acting forces.
There also exists a need for a switch which includes at least two independent sensing means to prevent total failure of the switch in the event that one of the sensing means ceases operation.
The present invention is directed to a redundant sensing edge for a door to protect persons, equipment and the door from impact damage by actuating a device upon force being applied to the sensing edge. The switch of the present invention is of relatively high profile and is sensitive to pressure being applied to any exposed surface of the sheath. In addition, the present invention overcomes the problems inherent in the conventional prior art sensing edges by incorporating an air impervious chamber having a pressure switch therein for sensing pressure change within the chamber, and a second chamber incorporating two sheets of electrically conductive material with a layer of non-conductive material therebetween for providing an additional sensing capability.